Minimizing battery wear in a hybrid energy storage system using a linear quadratic regulator

A battery-ultracapacitor Hybrid Energy Storage System (HESS) combines the advantages of both Li-ion batteries and ultracapacitors. Li-ion batteries sustain a relatively long electric only driving range but degrade if exposed to high C-rates and large number of cycles. Ultracapacitors are robust, have a quasi infinite cycle life and can sustain highly dynamic power profiles. This paper proposes a HESS Linear Quadratic Regulator (LQR) design to mitigate issues related to battery wear and peak power demands for electric and hybrid electric vehicles. The LQR controller imposes the battery current with a bidirectional power electronic converter that interfaces the battery to the ultracapacitor. The HESS is accurately modeled using experimental battery and ultracapacitor data in conjunction with equivalent circuit models. Simulations are carried out to validate the LQR controller on a UDDS drive cycle. Reduced battery wear is quantified using a spectral analysis of the battery current, which identifies microcycles.